Thermocouple



Aug. 7, 1945. H. s. JONES 2,381,058

THERMOCOUPLE Filed Dec. 9, 1941 9 9 9 FIG.2.

F IG.3.

INVENTOR.

HARRY S. JONES A V ORNEY proper positions with respect/ to each Patented Aug. 7, 1945 NITED STATES PATENT OFFICE Harry s. Jones, Washington, D. c., assignor to The Brown Instrument Company, Philadelphia,

Pa., aeorporatlo'n of Pennsylvinia v i Application Decemberi), 1941, Serial No. 422,264

' e m. (or. 13H) lators that are commonly used to support and separate these wires.

It is customary in the art to provide porcelain insulators for the wires of a thermocouple to hold these ,wires apart and to hold them in their other. These insulators can either take the form of beads which are adapted to receive a single wire or they can take the form of beads which are provided with parallel holes each oi which ,is adapted to receive one of the wires of the thermocouple. Generally speaking these porcelain beads are not pressed tightly against each other over the. wires since some slack is necessary in order for the thermocouples to be bent or otherwise guided when being placm in a protecting tube or direct '13 into a container whose temperature is to be measured.- It has been found that quite often thermocouple failures occur-due to breakage of the thermocouple wires between these porcelain insulators or beads. This failure is due to the fact that the wires are worn away or eroded to such an extent that they snap apart. The reason for this wearing away of the wires between the.

porcelain insulators is due several things one of which is the fact that in frequency vibrations often occur which vibrations actto chip oil small particles or porcelain which have the effect ltnother possible reason for failure of the wires is that they are e sed to they atmosphere or other gases at high temperature and these gases corrode the wire between the insulating beads where the wire is exposed to the'atmosphere. Even when the thermocouple is in a, protecting tube the action of these gases is present since reference should be had to the accompanying dra and descriptive matter in which'ls illustrated and described apreferred embodiment of the invention.

In the drawing:

g. l is a view, partly in section, of a thermocouple bodying my improvement, thethermocouple being mounted in a protecting tube,

Fig. Zis an enlarged section view of a portion oi the thermocouple, and

Fi 3 is a view showing the manner in which the wires of the thermocouple are eroded without the use of the washers of my invention.

Referring first to Fig. 1 there is shown a Protecting tube i for, a thermocouple, which tube is provided with a threadedcollar 2 that serves to attach the protecting tube to a. wall through which the thermocouple is to extend. Attached to the end of the protecting tube is a head 3 pro- 4 of sand blasting the wire and thereby breaking it.

most metaisare more or less porous at high tem- It is an object of my invention to provmetm shims or washers between'the insulating memhere which surround the thermocouple wires.

: These washers serve toprotect the thermocouple .wires from "the eflects of the atmosphere and serve to prevent porcelainchips' from the insulators from eroding the wire between the insulators.

- v The various features of novelty; which char-ac terlze this invention are pointed outwith parin the claims annexed to and forming I a part of this-specification. For a. better understanding the invention. however, ltsyadvan-i and specific objects obtained with its use; 55 and inwhich wires that are not protected by the .insulators. g This unprotected portion of the wire isoften vided with a removable cover 6 which serves to protect a terminal block 5 for the thermocouple. Fastened in this terminal block are the ends of the thermocouplewires 6 and l, which at their other ends are Joined to form a hot-junction B. The wirw 6 and 7 of the thermocouple between the te n1 1 5 and the hot-junction d are separated ifrom each other and'from the protecting tube by. means of porcelain insulators e. The insulators each have a pair of holes through which the wiresextend.

Because oi the fact that the wires at have to be bent and should have some flexibility, it is not customary to force the insulating members 8 tightly against each other. This permits a flexibility of the thermocouple which isdesirable and necessary: Another reason for not forcing the insulators 8 tightly against each other is that they are usually made of someeeramic' such as.

porcelain and it they abut each other" they will the insulators do not closely abut each other there are portions of each of the thermocoupleeaten away as shown at ll in Fig; 3 either by corroeive gases in which the thermocouple'is immersed or by the small particles of porcelain which are chipped on of the insulating blocks -l and which. serve to act on the exposed portion 5010! the wires in a manner similar to sand-blasting to thereby wear these wires away. This sandblasting eflectfls probably produced by, high frequency vlbrationswhich' are set up inthe mocouple elements as a result of vibrations oi the times the thermocouple is used. In any event. a large percentage of thermocouple failures occur due to the erosion of the wires as shown at II.

In orde. to overcome this type of failure in thermocouples I have inserted in between each of the insulating members 9 a series of washers II which washers serve to prevent exposure of the thermocouple wire between the insulating members. These. washers should be made of some material which will withstand the temperature to which the thermocouple is to be subjected and which will not have any chemical eflect on the thermocouple wires. I have found that mica or felted asbestos serves admirably for this purpose. When the thermocouple is to be rigidly mounted and there will be little or no bending of the same the washers ll may well be made of mica. ThiSHSUbStQ-DOG is an excellent insulator and when made in washer form will effectively cover the normally exposed portions of thermocouple wire. Felted asbestos, is generally somewhat soi'ter than mica and is, therefore, more to be preferred for the washers it the thermocouple wires will have to be bent. Washers oi the latter type are slightly compressible and will give as the wires are bent." In either case the washers will completely protect the wires and will give enough to allow for normal movement of the wires and insulators relative to each other.'

It will be seen that .I have provided a means for Protecting a thermocouple wire'in, between the porcelain insulators that are placed over the same and have, therefore, provided an eflective means to prevent thermocouple failure due to the erosion or eating away of the' wires between "these insulators.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of this invention now known to merit would be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of this invention as set forth in the appended claims,

and that in some cases cerain features of this in-' ,vention may sometimes be used to advantage without a corresponding use of otherfeatures.

, Having now described this invention, what I claim as new 1. The combination with a thermocouple consisting of a pair of wires, 3. series 'oi' insulating members surrounding and separating said wires and a plurality of resilient, non-conducting, heatresisting washers filling the space along each wire between the insulators.

2. In combination with a thermocouple com, prising a pair of wires joined at one end, insulating members of a ceramic material mounted on said wires and being separated from each other, and washers of a resilient non-conducting and heat-resistant material mounted on said wires between the insulating members to flll up the space between said members whereby none v of the wire between said members will be exposed.

3. In combination with a temperature measuring element comprising a plurality of wires joined at'one end, a plurality of piecesof rigid insulating material surrounding said wires with a space between each of 'said pieces, and washers 01' a resilient, heat resisting, and non-conducting material surrounding said wires between said pieces of. insulating material whereby none of the wire is exposed.

4. In combination with a thermocouple having a pair of wires joined at one end, rigidceramic insulators mounted on said wires to insulate and separate them from each other, and a plurality of mica washers between each insulator, to separate the same and to cover the portions of the wires that would otherwise :he exposed between I temperature measuring element comprising a plurality of wires joined together at one end, of a plurality of rigid insulating members subject to chipping surrounding said wires, and a plurality of resilient,

non-conducting and heat resisting washers surrounding said 'wires in between each of said insulating members whereby said members cannot engage each other. I

" HARRY ,S. JONES. 

